1. Technical Field
This invention relates to polymers and more particularly to methods of reducing residual monomers present in polymer matrices.
2. Background of the Art
In the polymerization of a variety of thermoplastic materials it is generally difficult to obtain 100 percent monomer conversion. This means that there is usually some proportion, generally a few percent at most, of unreacted monomer remaining in the final polymer. This unreacted, or residual, monomer may cause problems during subsequent monomer processing or when the monomer is used to prepare an end use article. Such problems include migration or volatilization of the residual monomer, which may result in sticky pellets, poor surface quality in the end use article, problems with environmental standards, and the like.
One such polymer is polystyrene, which enjoys a wide variety of uses in articles formed via extrusion, milling, molding, drawing, blowing, and the like. In manufacturing polystyrene compositions, it is well known that free, unconverted styrene monomer remains absorbed within the polymer particles where polymerization is not 100 percent complete. Recently government regulatory agencies have moved toward establishing maximum permissible levels of various monomers in the environment on grounds that excessive levels may constitute a health hazard. These regulations may apply particularly to packaging materials intended for contact with environmentally sensitive products such as food, beverages, pharmaceuticals, cosmetics and the like, for which applications styrenic copolymers are especially suited.
Accordingly, it would be desirable in the art to identify a method of reducing the presence of residual styrene that can be used either before or during compounding.